Interesting idea ! Some questions:
-what's the psycho-acoustic rationale of "FR slope = 'Pink' ~3 dB/octave: BW~60-800Hz" ? Making sure you induce a simulated far reflection only in the ITD range and avoid the "filler" speakers to attract attention on them ?
- what does "visually in a straight line behind" exactly mean ? a horizontally spread array of in-wall speakers from the L to the R loudspeaker ?
- how does it sound ? Did you try it yourself ?

This is not what I meant. If you use such a device you are adding reverb or changing the recording quite a lot. I wondered if the original depth in the recording can be magically removed or enhanced. I guess no such device is possible?

Dipole speakers. Only for enhancing (or restoring) though, not removing, and not so much magical. :-)

I'd say from experience with my set;
#1: use dipole speakers (in a not too damped room)
#2: place woofers against the sidewalls (using an OSD placement might be even better but I'd have to build 4 extra towers/stands)
#3: use active crossovers/amplification and don't be afraid to use an equalizer (in moderation of course)

I fail to see a qualitative difference between using a reverb and using speakers which spread their sound all over the place in an only lightly (or not at all) damped room.
Except that a reverb is more controllable.

Working with a two-way speaker system, and the cross-over frequency equals about 2 kHz, it is possible to reflect the sound of the tweeter off of a nearby reflector that can be maybe 12" wide by 10" high towards the listening position. Assuming that you set the radius of curvature (concavity) of the reflector and the distance of the tweeter from the reflector correctly, then the sound of the speaker seems to originate from a point behind the speaker.

A conventional speaker will place sounds in between the speakers, or behind them by reproducing cues of the original acoustic space in the recording. Most people prefer this done well and room treatment can allow you to adjust the balance of direct to reflected sound.

Dipoles increase the sound stage depth due to the strong front wall reflection - basically they are creating a secondary phantom acoustic source - imagine that the front wall were a tinted glass mirror. The sound stage is made artifically deeper. It can be a desirable effect, especially with classical music where a live source is being reproduced that is much larger than the listening room. However, in other situations where you want a focused sharp image, dipoles don't perform as well. You don't get the same pinpoint imaging - I find that I notice it with vocals and HT use quite a bit. In other words, you pay a price to achieve this effect and you have to ask if it's really what you want.